1. Field of the Invention
The invention generally relates to permanent-split capacitor motors and, in particular, to a 2-pole/4-pole motor having a shared main winding and a shared auxiliary winding between the 2-pole configuration and the 4-pole configuration.
2. Description of the Prior Art
PSC motors, as one kind of single-phase induction motors, come in various multiple configurations and various pole configurations. One common configuration is a 2-pole/4-pole motor which operates at about 3,600 rpm at 60 Hz in the 2-pole configuration and which operates at about 1,800 rpm at 60 Hz in the 4-pole configuration. Such motors are often used as part of a hermetically sealed compressor to drive the compressor at two speeds, both a low speed and a high speed, to provide efficient compressor operation.
Within the limited space of the compressor, to provide the highest motor efficiency for a certain output power, one needs to make the best use of the active material, i.e., copper and steel. Sharing windings between 2-pole and 4-pole configurations is an important approach to achieve this. However, in the past, it has been believed that 2-pole/4-pole PSC motors can only share a main winding between the 2-pole and 4-pole configurations. It was believed that 2-pole/4-pole motors could not share both the main and auxiliary winding at the same time because it could not keep the phase shift between the main and auxiliary windings equal to 90.degree. for both the 2-pole and 4-pole configurations. In particular, if both main and auxiliary windings are shared and the auxiliary winding has 90.degree. phase shift with the main winding in the 2-pole mode, the phase shift in 4-pole mode becomes 180.degree.. If the auxiliary winding has a 90.degree. phase shift with the main winding in the 4-pole mode, the phase shift in 2-pole becomes 45.degree.. When a phase shift between the main and auxiliary windings is equal to 180.degree., the motor cannot start. When a phase shift is equal to 45.degree., the motor performance is generally poor. Therefore, the prior art has generally employed a separate auxiliary winding in each configuration for a PSC motor having 2-pole and 4-pole operating modes or configurations, to keep the phase shifts between the main and auxiliary windings both equal to 90.degree..
Therefore, there is a need for a 2-pole/4-pole PSC single phase motor with a shared main winding which also has a shared auxiliary winding.